1. Field of the Invention
This invention is in the field of processing agglomerated raw material for the manufacture of cement which involves drying in a drying step, and subsequent thermal treatment in a combustion zone consisting of preheating, deacidification and sintering steps, coupled with a cooling step, and makes efficient use of the exhaust gases from the combustion step.
2. Description of the Prior Art
In the typical method used for the production of cement clinkers, the raw material is passed to cyclone preheaters connected in series and then is calcined in comminuted form to clinkers in a rotary kiln. It frequently happens, however, that the raw material has a very high moisture content so that the preparation of raw material for cement from such high moisture content material is practical only by means of wet procedures. In such procedures, the raw materials are ground wet and homogenized in large slurry silos, resulting in a raw slurry for cement with a water content of approximately 36%. Through the use of filter presses and/or drum filters, it is possible to lower the water content to below about 22%. The remaining water removal may then take place before the actual calcining process by other thermal dehydration means. The raw material agglomerates because of their water content cannot be treated directly in the known calcining process utilizing cyclone preheaters and a rotary kiln.
For the purpose of drying the agglomerated raw material in known cement production installations, the raw material partially dehydrated in a filter press is comminuted in a mixing assembly and then delivered to a stream dryer such as a suspension gas dryer. The raw material leaves this dryer sufficiently dried in the form of gravel with a relatively small amount of coarse grains present. This raw material is then delivered to a storage bunker. It is withdrawn from storage in weighed dosages and then fed to the cyclone preheater which is connected in series with the rotary kiln. For reasons of economy, the exhaust gases from the furnace system are utilized as heating gases in the suspension gas dryer.
The method and apparatus of the prior art thus require additional capital investment and considerable processing if cement raw material of good quality is to be obtained.